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The Apollo Abort Guidance System (AGS, also known as Abort Guidance Section) was a backup computer system providing an abort capability in the event of failure of the Lunar Module's primary guidance system (Apollo PGNCS) during descent, ascent or rendezvous. As an abort system, it did not support guidance for a lunar landing. The AGS was designed by TRW independently of the development of the Apollo Guidance Computer and PGNCS. It was the first navigation system to use a strapdown Inertial Measurement Unit rather than a gimbaled gyrostabilized IMU (as used by PGNCS).〔(Computers in Spaceflight: The NASA Experience -- Chapter Two: Computers On Board The Apollo Spacecraft )〕 Although not as accurate as the gimbaled IMU, it provided satisfactory accuracy with the help of the optical telescope and rendezvous radar. It was also lighter and smaller in size. ==Description== The Abort Guidance System included the following components:〔(The Abort Guidance System (AGS) )〕 * Abort Electronic Assembly (AEA): the computer * Abort Sensor Assembly (ASA): a simple strapdown IMU * Data Entry and Display Assembly (DEDA): the interface similar to DSKY The computer used was MARCO 4418 (MARCO stands for Man Rated Computer) whose dimensions were 5 by 8 by 23.75 inches (12.7 by 20.3 by 60.33 centimeters); it weighed 32.7 pounds (14.83 kg) and required 90 watts of power. Because the memory had a serial access it was slower than AGC, although some operations on AEA were performed as fast or faster than on AGC. The computer had the following characteristics: * It had 4096 words of memory. Lower 2048 words were erasable memory (RAM), higher 2048 words served as fixed memory (ROM). The fixed and erasable memory were constructed similarly so the ratio between fixed and erasable memory was variable. * It was an 18-bit machine, with 17 magnitude bits and a sign bit. The addresses were 13 bits long; MSB indicated index addressing. * Data words were two's complement and in fixed-point form. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Apollo Abort Guidance System」の詳細全文を読む スポンサード リンク
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